Communication method, communication system, and output equipment

ABSTRACT

In order to prevent interruption of processing at the time when the format of data changes during transmission of streaming data over an IEEE 1394 or other network, when streaming data output from first equipment is caused to be received by second equipment via a prescribed network, when the streaming data output from the first equipment changes from content A in a first format to content B in a second format, after the end of output of content B invalid data in the same format as content B is output, and during output of this invalid data the first equipment investigates the state of the second equipment (steps S 11  to S 14 ); when it is detected that preparations for input of streaming data in the second format are completed, output of content B in the second format is begun.

TECHNICAL FIELD

[0001] This invention relates to a communication method andcommunication system suitable for application when transmitting audiodata and other streaming data between equipment connected by, forexample, an IEEE (Institute of Electrical and Electronics Engineers)1394 bus line, as well as to output equipment used by this communicationsystem.

BACKGROUND ART

[0002] Audio and video equipment is being developed which is capable ofbidirectional transmission of information via networks using an IEEE1394 serial data bus. When transmitting data over such a bus, anisochronous transfer mode, used for realtime transmission ofcomparatively large quantities of video data, audio data and similar,and an asynchronous transfer mode, used for reliable transmission ofstill images, text data, control commands and similar, are provided, anddedicated frequency bands are used for each of these modes intransmission.

[0003]FIG. 1 is a diagram showing an example of connections using suchan IEEE 1394 bus; source equipment a, which is equipment sending data,input equipment (sink equipment) b, which is equipment receiving datasent from the source equipment a, and a controller c which controls datatransmission between the equipment a and b, are connected by an IEEE1394 bus d. At this time, when for example audio data is to betransmitted between the equipment a and b under control of thecontroller c, the controller c secures an isochronous transfer channelon the bus d, and after establishing a connection between the equipmenta and b to enable transmission over this channel, causes transmissionfrom the source equipment a to the input equipment b to be initiated.The source equipment a or the input equipment b may also serve as thecontroller.

[0004] When transmitting data between the source equipment a and inputequipment b in this way, a transmission method, in which controlcommands in what is called an “AV/C command transaction set” are used,is applied to, for example, audio and video equipment. The details ofthe AV/C command set are described in the “AV/C Digital InterfaceCommand Set General Specification,” published by the 1394 TradeAssociation.

[0005] When transmitting audio data or other streaming data from sourceequipment to input equipment, processing must be performed by the inputequipment according to the type of streaming data transmitted. Hencewhen there are changes in the format or other parameters of thestreaming data during transmission, this must be detected by the inputdata, and switching processing must be performed to change theprocessing state.

[0006]FIG. 2 is a diagram showing one example in which the data formatchanges during transmission of streaming data via a bus line. Supposefor example that the source equipment a is a disc reproductionapparatus, and that audio data (streaming data) comprising content A andcontent B is recorded on the disc from which data is being reproduced bythe disc reproduction apparatus. Suppose that content A and content Bare content recorded as audio data for output as streaming data indifferent formats. Further, suppose that the input equipment b processesthe input audio data for output, and is provided with the functions ofan amplifier to output the data to a connected speaker or similar. Insuch a configuration, streaming data reproduced by the source equipmenta from the disc is transmitted to the input equipment b via the busline.

[0007] Suppose that in such transmission, reproduction of content A endsat time ta, and processing proceeds to reproduction of content B. Atthis time, the input equipment b must change the settings of internalcircuitry and similar from the processing state for processing ofcontent A to the processing state for processing of content B, and sothe audio of content B is output from the speaker at the time tb atwhich these preparations are completed.

[0008] Hence during the interval from time ta, at which the formatchanges, until time tb, the audio of content B is not output, and so theproblem of loss of the beginning of the content occurs.

[0009] Such problems are particularly prominent when what is called ratecontrol (flow control) processing is executed between the sourceequipment and the input equipment. FIG. 3 is a diagram showing a statein which rate control is performed. This rate control is flow controlprocessing to adjust the rate at which streaming data is output from thesource equipment a, in keeping with the rate of processing of thestreaming data by the input equipment b. In this example, the inputequipment b comprises a buffer memory m which temporarily accumulatestransmitted streaming data; the input equipment b sends rate controldata to the source equipment a such that the amount of data accumulatedin this memory m is substantially constant, and the source equipment acontrols the output rate based on this rate control data when sendingstreaming data to the input equipment b.

[0010] In this case, when the format of the input data changes, if thebuffer memory m does not output all the data accumulated in the memoryto temporarily empty the buffer, data in another format cannot beaccumulated. For this reason, when there is a change in format fromcontent A to content B as shown in the above-mentioned FIG. 2, dataaccumulated in the memory m at time ta at which the format of thetransmitted data changes must all be output before the content B can beinput. Hence when control such as rate control is being executed, thereis the problem that a comparatively long time is necessary before thechanged format can be accommodated (that is, the time interval from timeta to time tb in FIG. 3).

[0011] The explanation thus far has described problems for the case oftransmission of streaming data over a network connected by an IEEE 1394bus line; but when transmitting streaming data over other networks,similar problems occur if the format of the streaming data changes.

DISCLOSURE OF THE INVENTION

[0012] This invention has as an object prevention of the interruption ofprocessing, when streaming data is transmitted over an IEEE 1394 orother network, at the time when there is a change during transmission inthe format of the streaming data.

[0013] A first invention is a communication method in which streamingdata output from first equipment passes through a prescribed network andis received by second equipment, wherein, when the streaming data outputfrom the first equipment is changed from streaming data in a firstformat to streaming data in a second format, the end of output ofstreaming data in the first format is detected, invalid data in the sameformat as the streaming data of the second format is output, and duringoutput of this invalid data, the first equipment investigates the stateof the second equipment, detects that preparations are completed forinput of streaming data in the second format, and thereafter initiatesoutput of streaming data in the second format.

[0014] By means of this method, when the first equipment detects thatsettings within the equipment which inputs streaming data via the bushave switched to enable reception of streaming data in the changedformat, output of actual streaming data from the first equipment isbegun. At this time, the second equipment guarantees that streaming datain the first format which has already been input is processed normally,and enables detection by the first equipment of the fact that settingswithin the second equipment have been changed. As a result, processingof streaming data in the first format is ended without interruption inthe second equipment, and streaming data in the second format can beprocessed correctly from the beginning, so that the received audio dataor other streaming data can be processed satisfactorily and withoutomissions.

[0015] A second invention is the communication method of the firstinvention, wherein, in order to investigate the state of the secondequipment, the first equipment sends a specific packet to the secondequipment over the network, and based on the response to this specificpacket, the first equipment confirms the state of the second equipment.

[0016] By means of this method, the first equipment can simply andreliably confirm the state of the second equipment.

[0017] A third invention is the communication method of the secondinvention, wherein the specific packet comprises data to query whetheror not the current state of the second equipment is a state enablinginput of streaming data in the second format, and the specific packet isrepeatedly transmitted until a state enabling input of streaming data inthe second format is confirmed, based on the response to this packet.

[0018] By means of this method, so-called polling processing can be usedto confirm the state of the second equipment.

[0019] A fourth invention is the communication method of the secondinvention, wherein the specific packet comprises data to causenotification that the second equipment has changed to a state enablinginput of streaming data in the second format, and the fact of a changeto a state in which streaming data in the second format can be input isconfirmed based on a response to this packet.

[0020] By means of this method, simply by sending a packet indicatingthe relevant notification, the first equipment can confirm the state ofthe second equipment.

[0021] A fifth invention is the communication method of the firstinvention, wherein the invalid data is data which causes audio output atthe second equipment to be muted.

[0022] By means of this method, during the interval in which thestreaming data format is changing, the audio output at the secondequipment can be reliably muted, and output of abnormal noise fromconnected speakers or similar can be reliably prevented.

[0023] A sixth invention is a communication system which causesstreaming data output from output equipment to be received by inputequipment over a prescribed network, wherein the output equipmentcomprises output equipment communication means to perform communicationover the network; streaming data acquisition means to acquire streamingdata output from the output equipment communication means; formatdetection means, which detects changes in the format of the outputstreaming data; and, output equipment control means, which controls theoutput of streaming data from the output equipment communication means,executes control such that invalid data is output from the outputequipment communication means in the same format as streaming data inthe second format when a change is detected in the output streaming datafrom a first format to a second format, investigates the state of theinput equipment through the output equipment communication means duringoutput of the invalid data, and, when it is detected that preparationsfor input of streaming data in the second format have been completed,begins output from the output equipment communication means of streamingdata in the second format; and wherein the input equipment comprisesinput equipment communication means to perform communication over thenetwork; format discrimination means to discriminate the format ofstreaming data received by the input equipment communication means;streaming data processing means to process streaming data received bythe input equipment communication means; and, input equipment controlmeans to set the processing of streaming data by the streaming dataprocessing means to processing compatible with the format of datareceived by the input equipment communication means, based on thediscrimination result of the format discrimination means.

[0024] By means of this system, when the output equipment detects thatsettings within the equipment which inputs streaming data via the bushave been changed to enable reception of streaming data in the changedformat, the output equipment begins output of actual streaming data, sothat the input equipment can correctly process streaming data in thechanged format from the beginning, and the received audio or otherstreaming data can be processed satisfactorily and without omissions.

[0025] A seventh invention is the communication system of the sixthinvention, wherein, in order to investigate the state of the inputequipment, the output equipment control means transmits a specificpacket from the output equipment communication means to the inputequipment, and, when the output equipment communication means receivesresponse data as a response to the transmitted packet, confirms thestate of the input equipment based on the received response data; and,when the input equipment communication means receives the specificpacket, the input equipment control means transmits data relating to thesettings in the streaming data processing means as response data fromthe input equipment communication means.

[0026] By means of this system, the state of the input equipment can besimply and reliably confirmed.

[0027] An eighth invention is the communication system of the seventhinvention, wherein the output equipment control means appends data tothe specific packet output from the output equipment communicationmeans, querying whether the state of the input equipment enables inputof streaming data in the second format; and, the input equipment controlmeans appends, to the response output from the input equipmentcommunication means, data enabling distinction of whether preparationsfor input of streaming data in the second format are completed.

[0028] By means of this system, so-called polling processing is used toenable confirmation of the state of the input equipment.

[0029] A ninth invention is the communication system of the sixthinvention, wherein the invalid data is data which causes audio output tobe muted by the streaming data processing means of the input equipment.

[0030] By means of this method, during the interval in which thestreaming data format is changing, the audio output at the inputequipment can be reliably muted, and output of abnormal noise fromconnected speakers or similar can be reliably prevented.

[0031] A tenth invention is output equipment, which outputs streamingdata to input equipment via a prescribed network, and comprisingcommunication means to perform communication over the network; streamingdata input means to input streaming data output from the communicationmeans; format detection means to detect changes in the format ofstreaming data output from the communication means; and, control meanswhich controls the output of streaming data from the communicationmeans, which, when the format detection means detects a change in theformat of the output streaming data from a first format to a secondformat, causes invalid data to be output from the communication means inthe same format as the streaming data of the second format, and which,when the completion of preparations for input of streaming data in thesecond format is detected during output of invalid data, causes theoutput of streaming data from the communication means in the secondformat to begin.

[0032] By means of this equipment, when the output equipment detects achange in settings within the input equipment so as to enable receptionof streaming data in the changed format, the output of actual streamingdata from the output equipment is begun, so that the input equipment cancorrectly process the streaming data in the changed format from thebeginning, and the received audio or other streaming data can beprocessed satisfactorily and without omissions.

[0033] An eleventh invention is the output equipment of the tenthinvention, wherein the control means, in order to investigate the stateof the input equipment, executes control so as to transmit a specificpacket from the communication means to the input equipment, and, when aresponse to the transmitted packet is received by the communicationmeans, discriminates the state of the input equipment from the datacontained in the response.

[0034] By means of this equipment, the state of the input equipment canbe simply and reliably confirmed.

[0035] A twelfth invention is the output equipment of the eleventhinvention, wherein the control means appends, to the specific packetoutput from the communication means, query data which queries whetherthe state of the input equipment is such that streaming data in thesecond format can be input, and executes control such that the specificpacket is repeatedly transmitted until it is confirmed, based on aresponse to a packet to which query data is appended, that the inputequipment is in a state in which streaming data in the second format canbe input.

[0036] By means of this equipment, so-called polling processing is usedto enable confirmation of the state of the input equipment.

[0037] A thirteenth invention is the output equipment of the tenthinvention, wherein the invalid data output from the communication meansis data which causes audio output to be muted at the input equipment.

[0038] By means of this equipment, during the interval in which thestreaming data format is changing, the audio output at the inputequipment can be reliably muted, and output of abnormal noise fromconnected speakers or similar can be reliably prevented.

BRIEF DESCRIPTION OF DRAWINGS

[0039]FIG. 1 is a configuration diagram showing an example ofconnections using an IEEE 1394 bus;

[0040]FIG. 2 is an explanatory drawing showing an example of aconventional case in which the format of streaming data changes;

[0041]FIG. 3 is a drawing showing an example of rate control;

[0042]FIG. 4 is a block diagram showing an example of a systemconfiguration in one aspect of this invention;

[0043]FIG. 5 is a block diagram showing an example of the internalconfiguration of a disc reproduction apparatus in one aspect of thisinvention;

[0044]FIG. 6 is a block diagram showing an example of the internalconfiguration of an amplifier apparatus in one aspect of this invention;

[0045]FIG. 7 is an explanatory drawing showing an example of thecyclical structure of data transmission on an IEEE 1394 bus;

[0046]FIG. 8 is an explanatory drawing showing an example of connectionsusing an IEEE 1394 bus;

[0047]FIG. 9 is an explanatory drawing showing an example of theconfiguration of a packet in isochronous transfer mode;

[0048]FIG. 10 is an explanatory drawing showing an example of theconfiguration of data transmitted using an AV/C command;

[0049]FIG. 11 is an explanatory drawing showing an example of an AV/Ccommand and response;

[0050]FIG. 12 is an explanatory drawing showing an example of processingof flow control in one aspect of this invention;

[0051]FIG. 13 is an explanatory drawing showing a transmission example(an example of a change in the sampling frequency) in one aspect of thisinvention;

[0052]FIG. 14 is an explanatory drawing showing an example of data in anAV/C input signal format status command;

[0053]FIG. 15 is an explanatory drawing showing an example oftransmission (an example of a change in the N flag) in one aspect ofthis invention;

[0054]FIG. 16 is an explanatory drawing showing an example oftransmission (an example of a format change) in one aspect of thisinvention; and,

[0055]FIG. 17 is an explanatory drawing showing an example oftransmission (an example of a change in the N flag) in one aspect ofthis invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0056] Below, one aspect of this invention is explained, referring toFIG. 4 through FIG. 17.

[0057] An example of the configuration of a network system to which thisinvention is applied is explained, referring to FIG. 4. This networksystem is a system which connects a plurality of equipment units via anIEEE 1394 serial data bus 9. Here, a disc reproduction apparatus 1,control apparatus 2, and amplifier apparatus 3 are connected by a bus 9,as shown in FIG. 4. As the control apparatus 2, for example, a personalcomputer can be employed.

[0058] Each of the equipment units comprises an IEEE 1394 bus connectorterminal, and implements functions enabling control by AV/C commands.The control apparatus 2 is equipment (a controller) which performstransmission control on the bus 9. Other equipment, not shown, which isconnected to the bus 9 may be configured to perform transmission controlon the bus 9, and the disc reproduction apparatus 1 or amplifierapparatus 3 may also comprise controller functions.

[0059] Seen in terms of functions stipulated by AV/C commands, each ofthe equipment units 1, 2, 3 can be seen as comprising a subunit whichexecutes processing to realize various functions, and a plug portion toperform input and output of data between the bus 9 and internal subunit.That is, the disc reproduction apparatus 1 comprises a control portion 1a which executes control functions, and a disc subunit 1 b whichperforms reproduction from a disc under control of the control portion 1a. The control apparatus 2 comprises a control portion 2 a whichexecutes control of transmission on the bus 9. The amplifier apparatus 3comprises a control portion 3 a which executes control functions, and anaudio subunit 3 b which performs processing and output of audio signals.The audio subunit 3 b is connected to speakers 3 d, 3 e. Further, theequipment units 1, 2, 3 respectively comprise plug portions 1 c, 2 b, 3c. Each of the plug portions 1 c, 2 b, 3 c implements a plurality ofplugs, and can be connected to a plurality of channels on the bus 9.

[0060]FIG. 5 shows one example of the internal configuration of a discreproduction apparatus 1. This disc reproduction apparatus 1 is anapparatus which reproduces digital audio data recorded on an opticaldisc 101. Optical discs 101 from which data can be reproduced by thereproduction apparatus 1 include, in addition to CDs (Compact Discs)DVDs (Digital Video Discs or Digital Versatile Discs) and other opticaldiscs on which data is recorded in audio and other formats.

[0061] The configuration of the disc reproduction apparatus 1 isexplained below. Data recorded on an optical disc 101 loaded into thereproduction apparatus 1 is read optically by an optical pickup 102, andthe signal read by the optical pickup 102 is supplied to and processedby a signal processing portion 103 to obtain reproduction data; afterconverting this reproduction data into an analog signal using adigital/analog converter 104, it is output from an analog outputterminal 105, and supplied to audio equipment or similar connected tothis terminal 105. Digital audio data not converted into analog form bythe digital/analog converter 104 is output from a digital outputterminal 106. Also, audio data reproduced from the disc 101 is suppliedto an IEEE 1394 bus interface 109, enabling transmission over theconnected bus 9.

[0062] Reproduction operation within the disc reproduction apparatus 1,and data transmission over the bus 9, are executed under control of acentral processing unit (CPU) 110. The CPU 110 is connected to memory111 which stores data necessary for control.

[0063]FIG. 6 shows an example of the internal configuration of anamplifier apparatus 3. The amplifier apparatus 3 comprises an inputterminal group 301, to which are supplied audio signals (digital oranalog signals) from a plurality of audio equipment units; audio signalsamong the plurality of audio signals obtained from this input terminalgroup 301 are selected by an input selection portion 302. Then thenecessary signal processing of the selected audio signals is performedby a signal processing portion 303. As signal processing, correction ofsignal characteristics, multichannel processing and other processing isperformed, for example using a digital processing circuit called a DSP(Digital Signal Processor). When the selected input signals are analogsignals, processing is performed after conversion into digital signalswithin the signal processing portion 303.

[0064] The output from the signal processing portion 303 is supplied tothe digital/analog converter 304 and converted into analog audiosignals, and the converted audio signals are supplied to a poweramplifier portion 305, and are amplified to an output capable of drivingspeakers. The output from the power amplifier portion 305 is supplied tospeakers connected via the speaker terminals 306, 307.

[0065] The amplifier apparatus 3 of this example comprises an IEEE 1394bus interface portion 308, and, when the interface portion 308 receivestransmitted audio data from the bus 9, enables supply of the receivedaudio data to the signal processing portion 303 via the input selectionportion 302.

[0066] Signal processing operation within the amplifier apparatus 3, andreception operation via the bus 9, are executed under control of thecentral processing unit (CPU) 309. The CPU 309 is connected to memory310 which stores data necessary for control.

[0067] Next, the state in which data is transmitted on the IEEE 1394 bus9 to which the above-described equipment is connected is explained. FIG.7 shows the cyclic structure of data transmission by equipment connectedvia an IEEE 1394 bus. On this IEEE 1394 bus, data is divided intopackets and is transmitted by a time-division method based on a cycle125 μs long. This cycle is created by a cycle start signal supplied froma node (an equipment unit connected to the bus) having cycle masterfunctions. An isochronous packet secures the bandwidth (expressed intime units, but called bandwidth) necessary for transmission of allcycles from the beginning. Consequently in isochronous transmission,transmission of the data within a fixed time is guaranteed. However,when a transmission error occurs there is no framework for protection,and so data is lost. During the time in each cycle not used forisochronous transmission, a node which has secured the bus as the resultof arbitration can employ acknowledge and retry messages in asynchronoustransmission of asynchronous packets to guarantee reliable transmission,but the transmission timing is not constant.

[0068] In order for a node (equipment) connected to the network toperform isochronous transmission, the node must support isochronousfunctions. Also, at least one node among the nodes connected to the IEEE1394 serial bus just have cycle master functions. Further, at least onenode among the nodes connected to the IEEE 1394 serial bus must haveisochronous resource manager functions.

[0069]FIG. 8 shows the relation between the plugs, plug controlregisters, and isochronous channels necessary for data transmission onthe bus. The audio-video devices (AV-devices) 11 to 13 are connected bythe IEEE 1394 serial bus. Among oPCR[0] to oPCR[2]. the transmissionrate and oPCR number of which have been stipulated by the oMPR of the AVdevice 13, isochronous data is transmitted over channel #1 of the IEEE1394 serial bus, specified by oPCR[1]. Among the iPCR[0] and iPCR[1],the transmission rate and iPCR number of which have been stipulated bythe iMPR of the AV device 11, by means of iPCR[0], the AV device 11reads the isochronous data transmitted over channel #1 of the IEEE 1394serial bus. Similarly, the AV device 12 transmits isochronous data overchannel #2 specified by oPCR[0], and the AV device 11 reads isochronousdata from channel #2 specified by iPCR[1].

[0070] Settings are made such that data transmitted from the output plugof the equipment that is the data transmission origin over the bus,using a channel secured in this way, can be received by an input plug ofthe equipment which is to receive the data. Processing to set thechannel and plugs in this way and establish a connection is executedunder control of prescribed equipment (a controller) connected to thebus.

[0071] In this way, data is transmitted between equipment connected byan IEEE 1394 serial bus. FIG. 9 shows an example of the data structureof packets when using an IEEE 1394 serial bus in isochronous transfermode to transmit streaming data.

[0072] In FIG. 9, packets are shown in units of quadlets (1 quadlet=32bits). The section of the first two quadlets is an isochronous packetheader, in which are placed, in addition to the data length, tag,channel and other data, a data error correction code CRC. The nexttwo-quadlet section is called the CIP header, and is a header used whentransmitting audio data and video data. In this CIP header are placed anSID, which is the node ID for the data transmission source (sourceequipment); the units in which the packet of streaming data isencapsulated DBS; the number of divisions prior to packet encapsulationFN; the number of quadlets added before data division QPC; the packetheader flag of the source equipment SPH; the counter used for detectionof packet losses DBC; and the signal format ID FMT.

[0073] There are also cases in which other data, which may support theformat of streaming data transmitted in the isochronous packet, isplaced in the CIP header. For example, the sampling frequency of audiodata, or a flag (N flag), described below, indicating that rate controlis being performed, may be placed in the header. In succession to a CIPheader configured in this way, a prescribed amount of streaming data isadded. At the end of the packet, an error correction code CRC is added.

[0074] Streaming data with a data structure like that described above istransmitted; but equipment connected via an IEEE 1394 serial bus alsotransmits commands, responses, and other control packets in asynchronoustransfer mode. In the system of this example, the AV/C commandsstipulated as commands for control of equipment connected via the IEEE1394 serial bus are used to enable control of each equipment unit andjudgment of equipment states. Data used in these AV/C commands isexplained below.

[0075]FIG. 10 shows the data configuration of packets when transmittingcommands and responses as AV/C commands. In the case of AV/C commands,commands and responses are transmitted in asynchronous transfer mode.AV/C commands are part of a command set to control audio and videoequipment, with CTS (command set ID)=“0000”. In order not to place aload on the bus or audio-video equipment, responses to these commandsare to be issued within 100 ms. The packet shown in FIG. 10 is alsoshown in units of one quadlet. The section of the beginning fivequadlets is the header portion of the packet; the remaining portion isthe data block.

[0076] The destination ID in the header portion indicates thedestination. CTS indicates the ID of the command set; for the AV/Ccommand set, CTS=“0000”. The ctype/response field indicates the functioncategory of a command when the packet is a command, and the commandprocessing result when the packet is a response.

[0077] In broad terms, four types of commands are defined: (1) commandswhich control functions from outside (CONTROL), (2) commands which querystates from outside (STATUS), (3) commands which query from outsidewhether there is support for control commands (GENERAL INQUIRY (supportfor opcodes) and SPECIFIC INQUIRY (support for opcodes and operands),and (4) commands which request notification of state changes (NOTIFY).

[0078] A response is returned according to the command type. Responsesto a CONTROL command are NOT IMPLEMENTED, ACCEPTED, REJECTED, andINTERIM (a tentative response). Responses to a STATUS command are NOTIMPLEMENTED, REJECTED, IN TRANSITION, and STABLE. Responses to GENERALINQUIRY and SPECIFIC INQUIRY commands are IMPLEMENTED and NOTIMPLEMENTED. Responses to a NOTIFY command are NOT IMPLEMENTED,REJECTED, INTERIM, and CHANGED. Commands and responses other than thosedescribed here may also be defined.

[0079] A subunit type is provided in order to identify the functionswithin the equipment; for example, “tape recorder/player”, “tuner” orsimilar types may be assigned. In order to perform discrimination whenthere exist a plurality of subunits of the same type, addressing isperformed using a subunit ID as a discrimination number. An opcoderepresents a command, and an operand represents a command parameter.“Additional operands” is a field which is added as necessary. “Padding”is also a field which may be added as necessary. “Data CRC” (CyclicRedundancy Check” is an error correction code used for error checkingduring data transmission.

[0080]FIG. 11 shows specific examples of AV/C commands. The left-handcolumn in FIG. 11 shows specific examples of ctype/response values. Inthe figure, the upper part lists commands, and the lower part listsresponses. “0000” is assigned to CONTROL, “0001” to STATUS, “0010” toSPECIFIC INQUIRY, “0011” to NOTIFY, and “0100” to GENERAL INQUIRY.“0101” through “0111” are reserved for future specifications. Also,“1000” is assigned to NOT IMPLEMENTED, “1001” to ACCEPTED, “1010” toREJECTED, “1011” to IN TRANSITION, “1100” to IMPLEMENTED/STABLE, “1101”to CHANGED, and “1111” to INTERIM. “1110” is reserved for futurespecifications.

[0081] In the center column of FIG. 11, specific examples of subunittypes are shown. “00000” is assigned to “Video Monitor”, “00011” to“Disk recorder/Player”, “00100” to “Tape recorder/Player”, “00101” to“Tuner”, “00111” to “Video camera”, “11100” to “Vendor unique”, and“11110” to “Subunit type extended to next byte”. “11111” is assigned toa unit; this is used when sending to the equipment itself, for examplewhen turning the power supply on and off.

[0082] In the right-hand column of FIG. 11, specific examples of opcodesare shown. An opcode table exists for each subunit type; here, opcodesfor the case in which the subunit type is “Tape recorder/Player” areshown. Also, operands are defined for each opcode. Here “00h” isassigned to VENDOR-DEPENDENT, “50h” to SEARCH MODE, “51h” to TIMECODE,“52h” to ATN, “60h” to OPEN MIC, “61h” to READ MIC, “62h” to WRITE MIC,“C1h” to LOAD MEDIUM, “C2h” to RECORD, “C3h” to PLAY, and “C4h” to WIND.

[0083] Using AV/C commands stipulated in this way, equipment connectedto the bus is controlled, and based on this control, data is transmittedbetween-equipment connected to the bus. The commands, responses, andsubunit types shown in FIG. 11 are representative, but others aredefined besides these, and in addition, other commands and subunit typesmay defined in future and assigned to as yet undefined values.

[0084] Next, a case in which audio data or other streaming data istransmitted between equipment connected to the network of this exampleis explained. In this example, the disc reproduction apparatus 1 is theaudio data output equipment (source equipment), and audio signals sentto the bus from this source equipment are received by the amplifierapparatus 3 which is the input equipment (sink equipment), and audio isoutput (acoustically broadcast) from the speakers 3 d, 3 e connected tothe amplifier apparatus 3.

[0085] In the case of this example, rate control is performed totransmit streaming data (audio data) from the disc reproductionapparatus 1 to the amplifier apparatus 3. First, the state in which thisrate control is performed is explained, referring to FIG. 12. The sourceequipment shown in FIG. 12 is equivalent to a disc reproductionapparatus 1 which outputs audio data to a network; the sink equipment isequivalent to an amplifier apparatus 3 to which audio data is input fromthe network. Data transmitted between the source equipment and sinkequipment for the purpose of rate control (commands and responses) isdata configured as the above-described AV/C commands.

[0086] First, the sink equipment (amplifier apparatus 3) sends a baseconfigure subfunction of a rate control command specifying the referencerate for rate control, to the source equipment (disc reproductionapparatus 1) (step S1), and the sink equipment 3 verifies a response tothis command (step S2). Next, the sink equipment 3 sends a sink selectsubfunction of a rate control command specifying execution of ratecontrol, to the source equipment 1 (step S3). On receiving this command,the source equipment 1 sends a response indicating that processing ofthe command was performed normally to the sink equipment 3 (step S4). Atthis time, the source equipment 1 becomes target equipment forsuccessful execution of rate control (command-based rate control), andstores the node ID of the amplifier apparatus 3 which is the controllerfor the rate control. By this means, the disc reproduction apparatus 1judges that the amplifier apparatus 3 which is the controller is theinput equipment for the streaming data which is controlled by ratecontrol.

[0087] Subsequently, when there is a need to change the rate oftransmission of streaming data through rate control, the amplifierapparatus 3 which is the controller sends a flow control subfunction ofa rate control command to the disc reproduction apparatus 1 (step S7),and verifies a response to this command (step S8). As the value of thedata for the rate specified by this command, a transmission rate is setwhich is appropriate to the state of internal signal processing of thestreaming data input to the amplifier apparatus 3. Also, while this ratecontrol is successfully continued, the amplifier apparatus 3 which isthe controller must repeatedly send a flow control subfunction of a ratecontrol command to the disc reproduction apparatus 1, at an arbitrarytime within a 5-second interval as a command interval. In FIG. 12, thisflow control subfunction is omitted. In this way, streaming data istransmitted via the bus line 9 in a state in which flow control isperformed with the amplifier apparatus 3 (the input equipment) as thecontroller.

[0088] After the disc reproduction apparatus 1 becomes the targetequipment for successful execution of this rate control, a path changesubfunction of an input select control command is sent to the amplifierapparatus 3 which is the input equipment for the streaming data (stepS5). On obtaining a response to this command (step S6), the discreproduction apparatus 1 confirms the input plug for streaming data ofthe amplifier apparatus 3, as well as the subunit connected internallyto this input plug, and the destination flag of the subunit.

[0089] Next, in a state in which audio data (streaming data) istransmitted from the disc reproduction apparatus 1 to the amplifierapparatus 3 via the bus line 9 in this way, processing when the formatof the audio data changes during transmission is explained. Here, it isassumed that two content types, content A and content B, are recorded onthe disc 101 data from which is reproduced by the disc reproductionapparatus 1, and in succession to reproduction of content A,reproduction operation to reproduce content B is performed. It isfurther supposed that in content A, audio data in a first format isrecorded, while in content B, audio data in a second format is recorded.

[0090] With respect to the difference between the first format of theaudio data of content A and the second format of the audio data ofcontent B, various changes are conceivable. For example, the audio datasampling frequency may change. Or, the number of channels may change.Even in cases where there is no change in the sampling frequency ornumber of channels, the data configuration may change due to differencesin audio data standards. As one change in the streaming dataconfiguration due to standard changes, for example, a change may occurfrom a format stipulated by IEC 60958 to a format stipulated as DVDaudio.

[0091] When such audio data format changes occur, there are cases inwhich, for example, as already explained in FIG. 10, values in the CIPheader added to isochronous transfer packets change to values of thecorresponding format, and there are cases in which the CIP header valuesdo not change even when the format changes.

[0092] To explain examples of processing in each of these cases, first,an example of a case in which the sampling frequency changes between afirst format and a second format, and data contained in the CIP headerand indicating the sampling frequency changes, is explained referring toFIG. 13.

[0093] In the example of FIG. 13, the content A has a sampling frequencySFC=X, and the content B has a sampling frequency SFC=Y. As is shown asthe disc reproduction state T11 of the source equipment, by reproducingthe content A using the disc reproduction apparatus 1, the audio data ofthe content A is output from an output plug oPCR of the source equipmentto the bus line 9 in isochronous transfer mode using a prescribedtransmission channel, as shown by the output state T12 of the outputplug oPCR of the source equipment; and, as is shown as the state T13 ofan input plug iPCR of the amplifier apparatus, this audio data is inputto the input plug iPCR of the amplifier apparatus 3, and, as indicatedin the audio output state T14 of the amplifier apparatus 3, the audio ofthe content A is output from the speaker apparatus connected to theamplifier apparatus 3. This is an example of the performance of ratecontrol, and in the amplifier apparatus 3, processing of input audiodata is performed after temporary accumulation in buffer memory; thusaudio is output to the speakers with a delay equal to the time ofaccumulation in the buffer memory.

[0094] Here, suppose that reproduction of content A ends at time t₁₁.Processing then proceeds to reproduction of content B; but at this timethe CPU 110 of the disc reproduction apparatus 1 judges that the formatsof the audio data of content A and content B are different, and so thedisc reproduction state is put into a reproduction paused state. Then,invalid audio data in the format of content A is output from the outputplug oPCR of the disc reproduction apparatus 1, to the channel to whichaudio data was being output. This content A “invalid data” is data whichis indicated to be ancillary data attached to audio data, and invalidaudio data (no-data). The format of the audio data is the same format asthe data of the content A.

[0095] This invalid audio data in the format of the content A is outputto the bus line 9 for a comparatively short time (for example, severaltens of milliseconds), from time t₁₁, at which reproduction of content Aends, until time t₁₂. Until this time, the format of the audio dataoutput is the same format as the audio data of the content A, and isdata with a sampling frequency SFC=X. As the invalid audio data, forexample, audio data with level 0 is used.

[0096] Then, at time t₁₂, invalid audio data in the format of content Bis output from the output plug oPCR of the disc reproduction apparatus1. Here too, the content B “invalid data” is data which is indicated tobe ancillary data attached to audio data, and invalid audio data(no-data). However, the audio data is audio data in the second format(data in the CIP header is also data in the second format), configuredsimilarly to content B data, and is data with sampling frequency SFC=Y.As this invalid audio data also, for example, audio data with level 0 isused.

[0097] As indicated by the state T13 in FIG. 13, as data input from theinput plug iPCR of the amplifier apparatus 3, input of the audio data ofcontent A ends at time t₂₁, and from time t₂₁ to time t₂₂, invalid audiodata in the format of the content A is input, and after time t₂₂,invalid audio data in the format of the content B is input. When audiodata in the format of content B is input, at time t₂₃, delayed slightlyfrom the time t₂₂ at which input is begun, the amplifier apparatus 3detects a change to the sampling frequency SFC=Y from the data relatingto sampling frequency contained in the CIP header of the transmitteddata.

[0098] When the state is then entered in which invalid audio data in theformat of the content B is transmitted to the bus line 9, the discreproduction apparatus 1 which is the source equipment sends an inputplug signal format status command, to investigate the state of an inputplug of the input equipment (step S11). Here the input plug the state ofwhich is being investigated is the input plug confirmed by the pathchange subfunction of the input select control command in step S5, shownin FIG. 12.

[0099] The command in step S11 has for example the configuration shownin FIG. 14. That is, data for [INPUT PLUG SIGNAL FORMAT], which is theapplicable command, is placed in the [opcode] section, data identifyingthe plug the state of which is to be investigated is placed in the[operand(0)] section, and the maximum value FF is placed in the[operand(1)] and subsequent sections. This data is inserted into thepacket configuration shown in FIG. 10.

[0100] When this command is transmitted from the disc reproductionapparatus 1 to the amplifier apparatus 3 via the bus line 9 as step S11,the amplifier apparatus 3 returns a response to this input plug signalformat status command to the disc reproduction apparatus 1 (step S12).In this response, the command data in the [opcode] and [operand(0)]sections of the command are left unchanged, and in [operand(1)] andsubsequent sections, data in the FMT and FDF sections of the CIP headerof data being input at that time at the subunit is inserted.

[0101] In the case of this example, when a response is sent in step S12of FIG. 13, the data of content A is still being output, as indicated bystate T14 in FIG. 13; consequently the FMT and FDF data of the CIPheader for the format of content A is returned, and so the discreproduction apparatus 1 confirms that preparations for input of contentB by the amplifier apparatus 3 are not completed.

[0102] Then, in the disc reproduction apparatus 1, with the currentstreaming data output (invalid data in content B format) maintained,each time a prescribed interval (for example, approximately 200 ms) haselapsed, the transmission of an input plug signal format status commandof step S11 is performed, and this is repeated until it can be confirmedthrough a response that preparations for input of content B data by theamplifier apparatus 3 have been completed. That is, polling processingis executed until it can be performed that preparations for content Binput have been completed.

[0103] In the example of FIG. 13, as indicated by the state T14 of FIG.13, at the end of the output of content A audio data accumulated in thebuffer memory at time t₂₄, switching of processing in the subunit so asto enable input of data with a sampling frequency SFC=Y is executed, andupon receiving an input plug signal format status command after time t₂₄(step S13), FMT and FDF data of the CIP header of data in the sameformat as the content B data being received is inserted into theresponse, which is transmitted (step S14).

[0104] When the response in step S14 is received by the discreproduction apparatus 1 at time t₁₃, after a prescribed interval (forexample, several tens of milliseconds) at time t₁₄, invalid data in theformat of content B output from the disc reproduction apparatus 1 ischanged to valid data in the format of content B. However, here a mutesignal with audio level 0 (no-sound state) is output for a comparativelyshort interval (for example, several hundreds of milliseconds) untiltime t₁₅. This mute signal streaming data can be discriminated as theformat of content B, and enables the amplifier apparatus 3 to make allinternal settings for signal processing, while also being data whichmutes the audio within the amplifier apparatus 3 as well as the outputthereof, and contains ancillary data attached to the audio data.

[0105] At time t₁₅, as shown by state T11 in FIG. 13, the reproductionpause of the disc 101 is cancelled by the disc reproduction apparatus 1,reproduction of audio data recorded as content B is begun, and as shownin state T12 of FIG. 13, output of content B audio data to the bus line9 from an output plug is begun.

[0106] The content B audio data which has begun to be transmitted inthis way is input at time t₂₅ to the amplifier apparatus 3, and at timet₂₆, somewhat later than time t₂₅ due to time required for accumulationin buffer memory and data processing, the mute state is canceled and theaudio of content B begins to be output from the speakers connected tothe amplifier apparatus 3.

[0107] When the format of transmitted audio data changes in this way,after the output equipment has confirmed that the input equipment canreliably process data in the changed format, transmission of content Baudio data is begun; hence content B can be reliably output from thebeginning portion, so that loss of the beginning of the content can beprevented. Further, content A, which is data preceding this change, canalso be output up to the end, so that there is no interruption duringprocessing of previously input data. Hence even if there is a change inthe format of streaming data being transmitted, complete loss-free datatransmission and processing can be performed.

[0108] In the example shown in FIG. 13, as processing to confirm thecompletion of preparations for data input from the disc reproductionapparatus 1 to the amplifier apparatus 3, an input plug signal formatstatus command is sent, and so-called polling processing is performed,repeating transmission of this command until the completion ofpreparations for input of content B can be confirmed through a response;however, a NOTIFY command, which is an AV/C command notifying of achange in the prepared state, may be used.

[0109] That is, as step S11, in place of an input plug signals formatstatus command, an input plug signal format notify command istransmitted. On receiving this notify command, in step S12 the amplifierapparatus 3 immediately returns an INTERIM response, which is a responseindicating the state at the time the command is received and whichacknowledges notification; then, when preparations for reception ofcontent B are completed immediately afterward at time t₂₄, CHANGED datawhich is a response indicating that the state has changed is sent. Uponreceiving this [CHANGED] data, the disc reproduction apparatus 1 judgesthat preparations for input of content B have been completed by theamplifier apparatus 3.

[0110] In the example shown in FIG. 13, at the time when reproduction ofcontent A ends, invalid data in the format of content A is brieflytransmitted; however, this invalid data in the format of content A maybe omitted, and immediately after the end of reproduction of content A,transmission of invalid data in the format of content B may be begun.Similarly, after sending invalid data in the format of content B, a mutesignal is transmitted for a prescribed interval, after whichtransmission of content B data is begun; however, transmission of thismute signal may also be omitted.

[0111] Next, an example in which the streaming data N flag changes isexplained, referring to FIG. 15. The example of FIG. 13 was an examplein which the sampling frequency changed; but changes in the streamingdata of transmitted content may also involve changes in the value of theN flag. As already explained, this N flag changes according to whetherthere is flow control (rate control); for example, the N flag=1 forstreaming data the transmission rate of which is being controlled byflow control, and the N flag=0 for streaming data the transmission rateof which is not being controlled by flow control. Here it is supposedthat the N flag=1 for content A, and that the N flag=0 for content B.This N flag data is further supposed to be included in the CIP header.

[0112] The state T21 of FIG. 15 is a state of disc reproduction of thesource equipment; as indicated in this state T21, by reproducing thecontent A using the disc reproduction apparatus 1, the audio data of thecontent A is output to the bus line 9 in isochronous transfer mode fromthe output plug oPCR using a prescribed transmission channel, as shownin state T22 (output plug state in the source equipment); as indicatedin state T23 (input plug state in the amplifier apparatus), this audiodata is input from the input plug iPCR of the amplifier apparatus 3, andas indicated in state T24 (audio output state of the amplifierapparatus), the audio of content A is output from the speakers connectedto the amplifier apparatus 3. The content A is streaming data thetransmission rate of which is controlled by flow control, so that in theamplifier apparatus 3, input audio data is temporarily accumulated in abuffer memory before being processed, and so the audio is output fromthe speakers after a delay equal to the time of accumulation in thebuffer memory.

[0113] Suppose that reproduction of content A ends at time t₁₁.Processing then proceeds to reproduction of content B; at this time, theCPU 110 of the disc reproduction apparatus 1 judges that the streamingdata (here, the N flag) of content A and content B is different, and soputs the disc reproduction state in a reproduction paused state. Then,invalid audio data in the format of content A is output, over thechannel to which audio data had been output, from the output plug oPCRof the disc reproduction apparatus 1. Here the invalid content A data isdata indicated to be ancillary data attached to audio data, and invalid(no-data) audio data. The format of the audio data is the same as theformat of content A data.

[0114] This invalid audio data in the format of content A is output fromthe time t₁₁′ at which reproduction of content A ends for thecomparatively short interval (for example, several tens of milliseconds)until time t₁₂′. The format of the output audio data is the same formatas the audio data of content A, and for this data the N flag=1. As theaudio data of this invalid data, for example, audio data with level 0(no-sound state) is used.

[0115] Then at time t₁₂′, invalid audio data in the format of content Bis output from the output plug oPCR of the disc reproduction apparatus1. Here the invalid data of content B is ancillary data attached toaudio data, and invalid audio data (no-data). The audio data is audiodata in the second format (and the CIP header is also data in the secondformat), configured in the same way as the data of content B, and withthe N flag=0. As the invalid audio data, for example audio data withlevel 0 is used.

[0116] As the data input from the input plug iPCR of the amplifierapparatus 3, as shown in state T23 of FIG. 15, at time t₂₁′ the input ofcontent A audio data ends, and from this time t₂₁′ to t₂₂′ invalid audiodata in the format of content A is input; after time t₂₂′, invalid audiodata in the format of content B is input. When audio data in the formatof content B begins to be input, the amplifier apparatus 3 detects, at atime t₂₃′ somewhat later than the time t₂₂′ at which input begins, thatthe N flag has changed to 0 and the transmission rate of the streamingdata is being controlled by flow control.

[0117] When a state is entered in which invalid audio data in the formatof content B is transmitted to the bus line 9, the disc reproductionapparatus 1 which is the source equipment sends an input plug signalformat status command in order to investigate the state of an input plugof the input equipment (step S11′). Here the input plug the state ofwhich is being investigated is the input plug verified by the pathchange subfunction of the input select control command in step S5 ofFIG. 12.

[0118] The command of this step S11′ is, for example, configured asshown in FIG. 14. That is, the data for [INPUT PLUG SIGNAL FORMAT],which is the relevant command, is placed in the [opcode] section, dataspecifying the plug the state of which is to be investigated is placedin the [operand(0)] section, and the maximum value FF is inserted intothe [operand(1)] and subsequent sections. This data is arranged in thepacket shown in FIG. 10.

[0119] When this command is transmitted from the disc reproductionapparatus 1 to the amplifier apparatus 3 over the bus line 9 as stepS11′, the amplifier apparatus 3 returns a response to this input plugsignal format status command to the disc reproduction apparatus 1 (stepS12′). In this response, the command data in the [opcode] and[operand(0)] sections are left unchanged, and the FMT and FDF sectiondata in the CIP header of data being input at that time by the subunitis inserted into the [operand(1)] and subsequent sections.

[0120] In the case of this example, at the time when a response is sentin step S12′ of FIG. 15, the data of content A is being output, asindicated by the state T24 of FIG. 15; consequently data is returnedindicating the state in which streaming data is being input with thetransmission rate controlled by flow control, and the disc reproductionapparatus 1 verifies that preparations for input of content B are notyet completed at the amplifier apparatus 3.

[0121] Then, while maintaining the current streaming data output(invalid data of content B), the disc reproduction apparatus 1 transmitsthe input plug signal format status command of step S11 ′ each time aprescribed interval elapses (for example, approximately 200milliseconds), and repeats this transmission until it can be confirmedthrough a response that preparations for input of content B have beencompleted by the amplifier apparatus 3. That is, polling processing isexecuted until it can be confirmed that preparations for input ofcontent B are completed.

[0122] In the example of FIG. 15, as indicated by the state T24 of FIG.15, when the output of content A audio data accumulated in the buffermemory ends at time t₂₄′, a switch to processing of data thetransmission rate of which is not controlled by flow control isexecuted, and when the input plug signal format status command isreceived after this time t₂₄′ (step S13′), data indicating a state inwhich streaming data the transmission rate of which is not controlled byflow control can be input is inserted into the response, which istransmitted (step S14′).

[0123] When the disc reproduction apparatus 1 receives the response ofstep S14′ at time t₁₃′, after a prescribed interval (for example,several tens of milliseconds) at time t₁₄′, invalid data in the formatof content B output at this time from the disc reproduction apparatus 1is changed to valid data in the format of content B. However, a mutesignal with audio level 0 (no-sound state) is output until time t₁₅′after a comparatively short interval (for example, several hundredmilliseconds) has elapsed. The streaming data of this mute signal can bediscriminated as the format of content B, and enables all internalsettings for signal processing to be made in the amplifier apparatus 3;in addition, the data causes muting within the amplifier apparatus 3 andof the audio output, and contains ancillary data attached to the audiodata.

[0124] Then, at time t₁₅′ the pause in reproduction of the disc 101 bythe disc reproduction apparatus 1 is canceled, as indicated by the stateT21 of FIG. 15, reproduction of the audio data recorded as content B isbegun, and as indicated in state T22 of FIG. 15, output of content Baudio data to the bus line 9 from the output plug is begun.

[0125] Content B audio data, transmission of which is begun as describedabove, is input from time t₂₅′ by the amplifier apparatus 3, the mutestate is canceled at time t₂₆′ after some time for data processing haselapsed from time t₂₅′, and content B audio begins to be output fromspeakers connected to the amplifier apparatus 3.

[0126] Thus even when there is a change in streaming data in which the Nflag changes, similarly to when the sampling frequency changes, completedata transmission and processing can be performed, without loss of thebeginning or other omissions.

[0127] In the example shown in FIG. 15, as processing to confirmpreparations for input from the disc reproduction apparatus 1 to theamplifier apparatus 3, an input plug signal format status command issent, and so-called polling processing is performed in whichtransmission of this command is repeated until it is confirmed by aresponse that preparations for input of content B are completed;however, the NOTIFY command, which is an AV/C command notifying of statechanges, may also be used.

[0128] In other words, as step S11′, in place of the input plug signalformat status command, an input plug signal format notify command istransmitted. On receiving this notify command, the amplifier apparatus 3immediately returns, in step S12′, the state at the time at which thiscommand was received, together with an INTERIM response which is aresponse acknowledging notification. Then, immediately after time t₂₄′when preparations for receipt of content B are completed, CHANGED datawhich is a response indicating a changed state is sent. When the discreproduction apparatus 1 receives this [CHANGED] data, it is judged thatpreparations for input of content B by the amplifier apparatus 3 arecompleted.

[0129] In the example shown in FIG. 15, when reproduction of content Aends, invalid data in the format of content A is transmitted briefly;however, this invalid data in the format of content A may be omitted,and transmission of invalid data in the format of content B may be begunimmediately after the end of reproduction of content A. Similarly, aftersending invalid data in the format of content B, a mute signal istransmitted for a prescribed interval, after which transmission ofcontent B data is begun; however, transmission of this mute signal maybe omitted.

[0130] The examples of FIG. 13 and FIG. 15 explained above are bothexamples in which the change in streaming data can be detected from theCIP header added to the streaming data; an example in which a change instreaming data cannot be detected from the CIP header is explainedbelow. The latter example is processing which can also be applied tocases in which changes can be detected in the CIP header.

[0131] First, FIG. 16 shows an example of a case in which the signalformat changes without a change in the CIP header. In this example,content A is IEC 60958 format audio data, and content B is DVD audioformat audio data.

[0132] As indicated in state T31 of FIG. 16 (the disc reproduction stateof the source equipment), when content A is reproduced by the discreproduction apparatus 1, the audio data of content A is output to thebus line 9 in isochronous transfer mode from the output plug oPCR usinga prescribed transmission channel, as shown by the state T32 in FIG. 16(state of the output plug of the source equipment); as indicated bystate T33 in FIG. 16 (amplifier apparatus input plug state), this audiodata is input from the input plug iPCR of the amplifier apparatus 3, andas indicated by state T34 in FIG. 16 (amplifier apparatus audio outputstate), the audio of content A is output from speakers connected to theamplifier apparatus 3. In the amplifier apparatus 3, the input audiodata is temporarily stored in buffer memory before being processed, andso the audio is output from the speakers after a delay equal to the timeduring which the data is accumulated in the buffer memory.

[0133] Suppose that reproduction of content A ends at time t₃₁.Reproduction of content B is then begun; but at this time, the CPU 110of the disc reproduction apparatus 1 judges that the formats of contentA and of content B differ, and the disc reproduction state is put into areproduction pause state. Then invalid audio data in the format ofcontent A is output from the output plug oPCR of the disc reproductionapparatus 1 to the channel to which audio data had been output. Thiscontent A invalid data is data which is indicated to be ancillary dataattached to audio data, and invalid audio data (no-data). The format ofthe audio data is the same format as the data of the content A.

[0134] This invalid audio data in the format of content A is output tothe bus line 9 until time t₃₂, a comparatively short time (for example,several tens of milliseconds) after the time t₃₁ at which reproductionof content A ends. Until this time, the format of output audio data hasbeen the same format as the audio data of content A, that is, IEC 60958format audio data. As this invalid audio data, for example, audio datawith level 0 is used.

[0135] Then, at time t₃₂, a packet without actual data, called an emptypacket, is transmitted using an isochronous packet for streaming datatransfer. Transmission of this empty packet is performed over aninterval of, for example, 1 ms or greater. Thereafter, at time t₃₃invalid audio data in the format of content B (that is, the DVD audioformat) is output from the output plug oPCR of the disc reproductionapparatus 1. This content B invalid data is data which is indicated tobe ancillary data attached to audio data, and invalid audio data(no-data). As this invalid audio data also, for example, audio data withlevel 0 is used. After invalid content B data is transmitted for aprescribed interval from time t₃₃, at time t₃₄ a mute signal with theformat of content B is transmitted. Here, the streaming data of the mutesignal can be discriminated as the content B format, and all internalsettings for signal processing can be made by the amplifier apparatus 3,while in addition the data mutes the amplifier apparatus 3 and theoutput audio, and includes ancillary data attached to the audio data.

[0136] As data input from the input plug iPCR of the amplifier apparatus3, as indicated by state T33 in FIG. 16, when content A audio data inputends at time t₄₁ invalid audio data in the format of content A is inputfrom time t₄₁ until time t₄₂, and from time t₄₂ until time t₄₃ emptypackets are input. After time t₄₃, invalid audio data in the format ofcontent B is input. When audio data in the format of content B begins tobe input, the change in data format of the input streaming data (whichhowever is invalid data) itself is directly detected within theamplifier apparatus 3. Here, data in the changed format is transmittedafter transmission of empty packets with no actual data, so that thechange in format can be detected in a comparatively short time.

[0137] When invalid audio data in the format of content B is transmittedto the bus line 9, the disc reproduction apparatus 1 which is the sourceequipment sends a signal source status AV/C command in order toinvestigate the state of the input equipment (step S21).

[0138] After transmitting this command, the disc reproduction apparatus1 verifies a response to this command (step S22). By verifying thisresponse, the state of the amplifier apparatus 3 is verified, and it isjudged whether the amplifier apparatus 3 is currently in a stateenabling acceptance of input data and has completed preparations fordata processing.

[0139] In the case of this example, when a response is sent in step S22of FIG. 16, data of content A is still being output, as indicated bystate T34 of FIG. 16; hence the disc reproduction apparatus 1 confirmsthat preparations for input and processing of content B by the amplifierapparatus 3 are not completed.

[0140] Then, while maintaining the current streaming data output (DVDaudio mute signal), the disc reproduction apparatus 1 transmits thecommand of step S21 each time a prescribed interval elapses (forexample, approximately 200 milliseconds), and repeats this transmissionuntil it can be confirmed through a response that preparations for inputand processing of content B have been completed by the amplifierapparatus 3. That is, repeated transmission of commands and responses isperformed through polling processing until it can be confirmed thatpreparations for input of content B are completed.

[0141] In the example of FIG. 16, as indicated by state T34 in FIG. 16,it is possible to end output of content A audio data accumulated inbuffer memory at time t₄₅ and to switch the internal circuitry of theamplifier apparatus and similar so as to enable processing of content Baudio data; for example, downmix coefficients for DVD audio areacquired, and the acquired coefficients are set. After switching toprocessing of the content B audio data is performed, when the signalsource status command of step S23 is received, the fact thatpreparations for input and processing of content B audio data arecompleted is transmitted in the response (step S24), and this isverified by the disc reproduction apparatus 1.

[0142] When the disc reproduction apparatus 1 receives the response ofstep S24, immediately afterward at time t₃₅ the mute signal which is atthat time being output from the disc reproduction apparatus 1 is halted,and as indicated in state T31 of FIG. 16, the pause in reproduction ofthe disc 101 at the disc reproduction apparatus 1 is canceled andreproduction of the audio data recorded as content B is begun; and asindicated in state T32 of FIG. 16, output of content B audio data to thebus line 9 from an output plug is begun.

[0143] Content B audio data, transmission of which is begun in this way,is input to the amplifier apparatus 3 beginning from time t₄₆, and at atime t₄₇ later somewhat than time t₄₆ due to time required for buffermemory accumulation and data processing, the mute state is canceled andcontent B audio is output from the speakers connected to the amplifierapparatus 3.

[0144] Thus even when the format changes but there is no change in theheader of audio data transmitted in this way, loss of the beginning ofcontent and other omissions are avoided, and complete data transmissionand processing can be performed.

[0145] In the example of FIG. 16 also, a NOTIFY command may be used inplace of a status command to provide notification of a state change inorder to confirm preparations for input from the disc reproductionapparatus 1 to the amplifier apparatus 3.

[0146] Also, in the example of FIG. 16 invalid data in the format ofcontent A is transmitted briefly when reproduction of content A ends;however, invalid data in the format of content A may be omitted, andtransmission of empty packets begun immediately after the end ofreproduction of content A. Similarly, invalid data in the format ofcontent B may be omitted.

[0147] Next, as an example in which a signal source status command isused with the CIP header changed, an example of a case in which the Nflag changes is explained referring to FIG. 17. It is supposed that thechange cannot be detected. In this example, it is supposed that contentA has an N flag=1, and content B has an N flag=0.

[0148] As indicated in state T41 of FIG. 17 (disc reproduction state inthe source equipment), when the disc reproduction apparatus 1 reproducescontent A, the content A audio data is output from the output plug oPCRto the bus line 9 in isochronous transfer mode using a prescribedtransmission channel, as shown by state T42 in FIG. 17 (source equipmentoutput plug state); and as indicated by state T43 in FIG. 17 (amplifierapparatus input plug state), audio data from the input plug iPCR of theamplifier apparatus 3 is input, and content A audio is output fromspeakers connected to the amplifier apparatus 3, as indicated in stateT44 of FIG. 17 (amplifier apparatus audio output state). Content A isstreaming data the transmission rate of which is controlled by ratecontrol, and so in the amplifier apparatus 3 the input audio data istemporarily accumulated in buffer memory before processing, and theaudio is therefore output from the speakers after a delay equal to thetime of accumulation in the buffer memory.

[0149] Suppose that reproduction of content A ends at time t₃₁′. At thistime, reproduction of content B then begins, and at this time, the CPU110 of the disc reproduction apparatus 1 judges that the flag isdifferent for content A and for content B and puts the disc reproductionstate into a reproduction paused state. Then, invalid audio data in theformat of content A is output from the output plug oPCR of the discreproduction apparatus 1 using the channel to which audio data had beenoutput. Here, content A invalid data is data which is indicated to beancillary data attached to audio data, and invalid audio data (no-data).The format of the audio data is the same format as the data of thecontent A.

[0150] This invalid audio data in the format of content A is output tothe bus line 9 from the time t₃₁′ at which reproduction of content Aends, for the comparatively short interval (for example, several hundredmilliseconds) until time t₃₂′. Until this time, the format of the outputaudio data is the same format as the audio data of content A, and isdata for which the N flag=1. As this invalid audio data, for example,audio data with level 0 is used.

[0151] Then, at time t₃₂′, a PACKET without actual data, called an emptypacket, is transmitted using an isochronous packet for streaming datatransfer. Transmission of this empty packet is performed over aninterval of, for example, 1 ms or greater. Thereafter, at time t₃₃′invalid audio data in the format of content B is output from the outputplug oPCR of the disc reproduction apparatus 1. This content B invaliddata is data which is indicated to be ancillary data attached to audiodata, and invalid audio data (no-data). As this invalid audio data, forexample, audio data with level 0 is used. After invalid content B datais transmitted for a prescribed interval from time t₃₃′, at time t₃₄′ amute signal with the format of content B is transmitted. Here, thestreaming data of the mute signal can be discriminated as the content Bformat, and all internal settings for signal processing can be made bythe amplifier apparatus 3, while in addition the data mutes theamplifier apparatus 3 and the output audio, and includes ancillary dataattached to the audio data.

[0152] As data input from the input plug iPCR of the amplifier apparatus3, as indicated by state T43 in FIG. 17, when content A audio data inputends at time t₄₁′ invalid audio data in the format of content A is inputfrom time t₄₁′ until time t₄₂′, and from time t₄₂′ until time t₄₃′ emptypackets are input. After time t₄₃′, invalid audio data in the format ofcontent B is input. When audio data in the format of content B begins tobe input, the change in data format of the input streaming data (whichhowever is invalid data) itself is directly detected within theamplifier apparatus 3 from the fact that the N flag in the CIP header ischanged to 0, and that the streaming data transmission rate is no longercontrolled by flow control. Here, data in the changed format istransmitted after transmission of empty packets with no actual data, sothat the change in format can be detected in a comparatively short time.

[0153] When invalid audio data in the format of content B is transmittedto the bus line 9, the disc reproduction apparatus 1 which is the sourceequipment sends a signal source status AV/C command in order toinvestigate the state of the input equipment (step S21).

[0154] After transmitting this command, the disc reproduction apparatus1 verifies a response to this command (step S22). By verifying thisresponse, the state of the amplifier apparatus 3 is verified, and it isjudged whether the amplifier apparatus 3 is currently in a stateenabling acceptance of input data and has completed preparations fordata processing.

[0155] In the case of this example, when a response is sent in step S22of FIG. 17, data of content A is still being output, as indicated bystate T44 of FIG. 17; hence the disc reproduction apparatus 1 confirmsthat preparations for input and processing of content B by the amplifierapparatus 3 are not completed.

[0156] Then, while maintaining the current streaming data output (mutesignal), the disc reproduction apparatus 1 transmits the command of stepS21 each time a prescribed interval elapses (for example, approximately200 milliseconds), and repeats this transmission until it can beconfirmed through a response that preparations for input and processingof content B have been completed by the amplifier apparatus 3. That is,repeated transmission of commands and responses is performed throughpolling processing until it can be confirmed that preparations for inputof content B are completed.

[0157] In the example of FIG. 17, as indicated by state T44 in FIG. 17,it is possible to end output of content A audio data accumulated inbuffer memory at time t₄₅′ and to switch the internal circuitry of theamplifier apparatus and similar so as to enable processing of content Baudio data; for example, downmix coefficients for content B areacquired, and the acquired coefficients are set. After switching toprocessing of the content B audio data is performed, when the signalsource status command of step S23 is received, the fact thatpreparations for input and processing of content B audio data, thetransmission rate of which is not controlled by flow control, arecompleted is transmitted in the response (step S24), and this isverified by the disc reproduction apparatus 1.

[0158] When the disc reproduction apparatus 1 receives the response ofstep S24, immediately afterward at time t₃₅′ the mute signal which is atthat time being output from the disc reproduction apparatus 1 is halted,and as indicated in state T41 of FIG. 17, the pause in reproduction ofthe disc 101 at the disc reproduction apparatus 1 is canceled andreproduction of the audio data recorded as content B is begun; and asindicated in state T42 of FIG. 17, output of content B audio data to thebus line 9 from an output plug is begun.

[0159] Content B audio data, transmission of which is begun in this way,is input to the amplifier apparatus 3 beginning from time t₄₆′, and at atime t₄₇′ later somewhat than time t₄₆′ due to time required for buffermemory accumulation and data processing, the mute state is canceled andcontent B audio is output from the speakers connected to the amplifierapparatus 3.

[0160] Thus even when there is a change in the N flag or other parts ofthe CIP header, loss of the beginning of content and other omissions areavoided, and complete data transmission and processing can be performed.

[0161] In the example of FIG. 17 also, a NOTIFY may be used in place ofa status command to provide notification of a state change in order toconfirm preparations for input from the disc reproduction apparatus 1 tothe amplifier apparatus 3.

[0162] Also, in the case of the example of FIG. 17 also, the invaliddata in the format of content A may be omitted, and transmission ofempty packets begun immediately after the end of reproduction of contentA. Similarly, invalid data in the format of content B may be omitted.

[0163] In the above-described aspect, an example was explained in whichthe transmitted streaming data is audio data, but application to casesin which other types of streaming data is transmitted is also possible.For example, application is also possible in cases where the transmittedstreaming data is video data.

[0164] In the above-described case of audio data, when the format of thetransmitted data changes, invalid data which causes the audio output tobe muted is transmitted; in the case of video data, for example, invaliddata is transmitted which causes the display resulting from video datainput by the input equipment to be erased, and the video display by thedisplay means comprised by the input equipment (for example, displaymeans connected to the input equipment) may be put into a temporarynon-display state when there is a change in format.

[0165] In the above-described aspect, the input equipment prepares forinput of content B, which is the data after the change, after firstending processing of content A which is the data prior to the change;however, a method may be used in which, in the case of input equipmentwhich completes preparation for input of content B during processing ofcontent A, the completion of preparations for input during processing ofcontent A can be detected by the output equipment.

[0166] Further, equipment application of which as source equipment,input equipment, and controller is possible is not limited to theequipment described in the above aspect, but application is possible tovarious types of equipment which can be connected to a network.

[0167] In the above-described aspect, the case of a network configuredusing an IEEE 1394 bus was explained; however, application to cases inwhich similar data is transmitted between equipment over other networksis also possible. In this case, a network which performs datatransmission may be used. As one network which performs wirelesstransmission, for example, application to Bluetooth (a trademark) ispossible.

[0168] Also, the network (transmission path) over which streaming datais transmitted, and the network (transmission path) used to investigatethe state of the input equipment, may be separate. For example, anetwork configured using an IEEE 1394 bus may be employed as the networkfor transmission of streaming data, and a network which performs controlby wireless transmission may be used for transmission of commands andresponses to investigate the state of the input equipment.

[0169] In the above-described aspect, functions to perform theabove-described processing are set in the respective equipment units;however, a program to execute similar processing may be distributed tousers employing some kind of media, with users made to deploy theprogram stored on the media on a computer or similar connected to anIEEE 1394 network in order to execute similar functions. As the mediaused, in addition to optical discs, magnetic disks and other physicalrecording media, media provided to users via the Internet or othercommunication means may also be employed.

[0170] INDUSTRIAL APPLICABILITY

[0171] By means of this invention, when source equipment detects thefact that settings internal to equipment which inputs streaming data viaa bus have switched to enable reception of streaming data in a differentformat, the output of actual streaming data from the source equipment isbegun, so that the input equipment can correctly process the streamingdata in the changed format from the beginning, and the received audiodata or other streaming data can be processed satisfactorily and withoutomissions.

1. A communication method, in which streaming data output from firstequipment passes through a prescribed network and is received by secondequipment; wherein when streaming data output from said first equipmentis changed from streaming data in a first format to streaming data in asecond format, the end of output of streaming data in said first formatis detected; invalid data in the same format as the streaming data ofsaid second format is output; during output of this invalid data, saidfirst equipment investigates the state of said second equipment, detectsthat preparations are completed for input of streaming data in saidsecond format; and, thereafter, output of streaming data in said secondformat is begun.
 2. The communication method according to claim 1,wherein, in order to investigate the state of said second equipment,said first equipment sends a specific packet to said second equipmentover said network, and based on the response to said specific packet,said first equipment confirms the state of said second equipment.
 3. Thecommunication method according to claim 2, wherein said specific packetcomprises data to query whether or not the current state of said secondequipment is a state enabling input of streaming data in said secondformat, and, said specific packet is repeatedly transmitted until astate enabling input of streaming data in said second format isconfirmed, based on the response to said packet.
 4. The communicationmethod according to claim 2, wherein said specific packet comprises datato cause notification that said second equipment has changed to a stateenabling input of streaming data in said second format, and the fact ofa change to a state in which streaming data in said second format can beinput is confirmed based on a response to said packet.
 5. Thecommunication method according to claim 1, wherein said invalid data isdata which causes audio output at said second equipment to be muted. 6.A communication system which causes streaming data output from outputequipment to be received by input equipment over a prescribed network,wherein said output equipment comprises: output equipment communicationmeans to perform communication over said network; streaming dataacquisition means to acquire streaming data output from said outputequipment communication means; format detection means, which detectschanges in the format of said output streaming data; and, outputequipment control means, which controls the output of streaming datafrom said output equipment communication means, executes control suchthat invalid data is output from said output equipment communicationmeans in the same format as streaming data in the second format when achange is detected in the output streaming data from a first format to asecond format, investigates the state of said input equipment throughsaid output equipment communication means during output of said invaliddata, and, when it is detected that preparations for input of streamingdata in said second format have been completed, begins output from saidoutput equipment communication means of streaming data in said secondformat; and wherein said input equipment comprises: input equipmentcommunication means to perform communication over said network; formatdiscrimination means to discriminate the format of streaming datareceived by said input equipment communication means; streaming dataprocessing means to process streaming data received by said inputequipment communication means; and, input equipment control means to setthe processing of streaming data by said streaming data processing meansto processing compatible with the format of data received by said inputequipment communication means, based on the discrimination result ofsaid format discrimination means.
 7. The communication system accordingto claim 6, wherein, in order to investigate the state of said inputequipment, said output equipment control means transmits a specificpacket from said output equipment communication means to said inputequipment, and, when said output equipment communication means receivesresponse data as a response to said transmitted packet, confirms thestate of said input equipment based on the received response data; and,when said input equipment communication means receives said specificpacket, said input equipment control means transmits data relating tothe settings in said streaming data processing means as response datafrom said input equipment communication means.
 8. The communicationsystem according to claim 7, wherein said output equipment control meansappends data to the specific packet output from said output equipmentcommunication means, querying whether the state of said input equipmentenables input of streaming data in said second format; and, said inputequipment control means appends, to the response output from said inputequipment communication means, data enabling distinction of whetherpreparations for input of streaming data in said second format arecompleted.
 9. The communication system according to claim 6, wherein theinvalid data output from said output equipment communication means isdata which causes audio output to be muted by the streaming dataprocessing means of said input equipment.
 10. Output equipment, whichoutputs streaming data to input equipment via a prescribed network,comprising: communication means to perform communication over saidnetwork; streaming data input means to input streaming data output fromsaid communication means; format detection means to detect changes inthe format of streaming data output from said communication means; and,control means which controls the output of streaming data from saidcommunication means, which, when said format detection means detects achange in the format of the output streaming data from a first format toa second format, causes invalid data to be output from saidcommunication means in the same format as the streaming data of thesecond format, and which, when the completion of preparations for inputof streaming data in said second format is detected during output ofsaid invalid data, causes the output of streaming data from saidcommunication means in said second format to begin.
 11. The outputequipment according to claim 10, wherein said control means, in order toinvestigate the state of said input equipment, executes control so as totransmit a specific packet from said communication means to said inputequipment, and, when a response to said transmitted packet is receivedby said communication means, discriminates the state of said inputequipment from the data contained in the response.
 12. The outputequipment according to claim 11, wherein said control means appends, tothe specific packet output from said communication means, query datawhich queries whether the state of said input equipment is such thatstreaming data in said second format can be input, and executes controlsuch that said specific packet is repeatedly transmitted until it isconfirmed, based on a response to a packet to which said query data isappended, that said input equipment is in a state in which streamingdata in said second format can be input.
 13. The output equipmentaccording to claim 10, wherein the invalid data output from saidcommunication means is data which causes audio output to be muted atsaid input equipment.